The shaft of a typical steam turbine is supported for rotation by one or more bearings arranged within a bearing case. Typical bearings used for this purpose are oil-lubricated, journal bearings, which are protected from contamination via a bearing case seal, such as a labyrinth seal or brush seal. The presence of humidity and increased temperatures at the bearing case seal location allows moisture and other impurities to migrate through conventional bearing case seals and eventually accumulate inside the bearing case, thereby contaminating the bearing lubricating oil and oil reservoir. All steam turbines, even standby service units, are vulnerable to damage to or contamination of the bearing lubricating oil, which leads to a general degradation of the lubricating properties of the oil and can result in premature failure of the journal bearings.
In order to avoid premature failure of the bearings, turbine operators must frequently drain the bearing lubrication systems and replace the lubricating oil. How frequent such servicing is required depends on the operating steam conditions, the wear of the steam and oil seal components, and the severity of the moisture accumulation within the bearing case. Servicing the bearing lubrication system can be rather time-consuming and often requires the turbine to be put off line, thereby losing valuable operating time and costs.
What is needed, therefore, is a bearing case seal assembly that reduces or entirely restricts the influx of moisture and contaminants into the bearing case.